DESCRIPTION: (Applicant's Abstract) This prospective study investigates the course of homelessness among adults with serious drug problems, and it tests the impact of service use on that course. The current project examines the roles that contact with formal community agencies broadly conceived to include general health, mental health, drug and alcohol treatment; criminal justice; and welfare agencies has in modifying the course of homelessness for adults with serious drug problems. Although drug disorders are disproportionately high among homeless adults, and particularly among homeless women, reliable and detailed data on specific drug problems and service use among homeless adults are rare. We do not know about drug consumption over time in this population: which drugs are used; how drug problems vary by gender, age, or race; or how contact with health or social services or social welfare agencies or the criminal justice system affect drug use or homelessness over time. What happens to individuals with drug problems once they become homeless? What factors affect who escapes from the streets, where they go, and how vulnerable they are to repeated homelessness? To address these questions, we will use a unique longitudinal database on homeless adults (N=564, 385 men and 179 women) that incorporates an extensive set of measures on drug use and abuse, drug dependence, and drug associated behaviors. We will document the nature, extent, and patterns of drug use and abuse in this population. Specifically, we will (1) examine the relationship between drug use and the course of homelessness, and (2) investigate the mediating effects of service utilization on this relationship. The proposed study has the potential to help identify strategies and interventions that would most benefit homeless adults with drug problems. In doing so, the proposed study addresses emerging agendas in drug epidemiology: the examination of drug use and abuse among special populations who are at high risk of drug problems, but who are unlikely to be captured in household studies.